This invention relates to an electrophotographic printing machine, and more particularly to a sheet handler having a swiveling cross roll assembly that registers and deskew sheet material.
Sheet handlers with registration systems are well known. Generally, the sheet handler have a defined path through which the sheet-like material is transported from one station of an imaging apparatus to another. Registration of documents in such paths is commonly accomplished by driving the sheet-like material to a registered condition against a registration edge. Common means for applying the driving force to move the sheet-like material to the registration edge include cross-rollers, a pinch roller, an angle ball on a belt or any other similar well known device. This particular invention is concerned with cross-rollers.
Sheet handlers are often employed to automatically transport sheet-like material, e.g., documents, copy sheet and the like, to and from processing stations in image processing devices, such as image input terminals and printers. The sheet handlers, for effectiveness, register the sheet-like material during transport thereof. Registration of the sheet-like material in such image processing devices permits accurate, repeatable and, thus, acceptable functioning of such devices.
Sheet handlers used with an image input terminal transport image bearing sheet-like material, commonly called a document, to an imaging station for recording the image into or onto another medium, e.g., electronic medium, an imaging surface, such as a photoconductive surface and the like. Document handlers used with these terminals have document registration means so that documents are presented for imaging in a registered form. Failure to register the documents in such systems result in a skewed image being recorded.
Often in printers, sheet handlers are used to transport sheet-like material, such as, cut sheets having an image recorded thereon. Again, registration means are provided in many printers, as failure to present a registered sheet to the imprinting station often results in a skewed image formed on the sheet and even missing portions of the image. Also, in printers, others processing stations, such as, stapling stations, binding stations, etc. are often provided and registration means in the sheet handler are provided to deliver registered sheet-like material thereto.
Registration of sheet-like material, in some instances, is accomplished through the use of cross-rollers. In these devices, the rollers generally contact each other in the sheet path at a nip through which the sheet-like material passes. The rollers are arranged to have a normal force between them and, thus, provide a lateral force on the sheet-like material passing through the nip. The cross-rollers are skewed to the direction of travel of the sheet-like material passing between the rollers laterally against a registration edge and normally along the path that is at some skew angle bisecting the path direction and the lateral direction.
Optimally, the lateral force on the sheet-like material provided by the cross-rollers is sufficient to move the sheet-like material to and against the registration edge but is insufficient to buckle the sheet-like material upon engagement. That is, the edge of the sheet-like material upon engagement with the registration edge slides along the registration edge, as it slips in the rollers in the lateral direction. In present systems, the normal force, coefficient of friction and skew orientation of the rollers determine the lateral force applied to direct the sheet-like materials passing therebetween. The beam strength of the sheet-like material in combination with the force applied to direct the sheet-like material determines whether the material moves to engage the registration edge and whether the material buckles upon engagement with the registration edge. Thus, there exists a need to provide a relatively simple, inexpensive and reliable means for remotely adjusting the cross-roll registration system to met requirements for all weights of sheet-like material.
Accordingly, it has been deemed desirable to overcome skew and registration problems encountered with different weights of paper, particularly those associated with a cross-roll registration systems.